It has been the customary practice in the art to formulate biologically active compounds with inert diluents to facilitate the application of such compounds to their end uses. In some cases, the final formulation is undertaken by the applicator or end user while in other cases the final formulation is an item of commerce. An example of the former situation is wettable powder. The active ingredient (biologically active compound) is preliminarily compounded with diluents and agents which promote its dispersibility in water. The end user then disperses this powder into water to form a suspension having some short term stability. It is unnecessary that such formulations when diluted with water have long term storage stability. All that is required or desired is that the suspension formed by the end user have sufficient stability to permit him to prepare it and apply it. There is no need that such a suspension have stability to freeze thaw cycles. Indeed, recent developments in this field, as reflected in U.S. Pat. Nos. 3,737,581 and 3,920,441, have been to increase the concentration of active ingredients in such formulations.
Propoxur has been promoted as a 70% wettable powder and a 13% liquid solution mixed in organic solvents. In both cases, the end user must combine the purchased product with water to form a suspension with limited chemical stability. The end user must use all of the diluted product within a few days or destroy the unused portion, a serious cost effect to the user. Propoxur has been also marketed and is still being marketed as a 1% solution in kerosene in pressurized spray containers for direct utilization by the end user, since most home owners prefer not to mix the pesticide and prefer a ready-to-use material.
For a long time, there has been an interest in developing a "ready-to-use" insecticidal formulation in which the solvent was water. Such a formulation would provide a means for the ever increasing cost of petroleum products as well as the decreasing availability of them and reduce and/or eliminate the flammability problems connected with the use of these pressurized sprays. It would facilitate the use of less expensive finger sprayers, such as commonly employed for window spray and permit a greater availability of the product to those users of lower economic means as well. The commodity plastics typically used in constructing such sprayers are subject to attack and deterioration by the petroleum products traditionally used in such formulations. The use of a water based solution of the said invention would now permit such use.
The difficulties in developing such water based final formulatons have been manifold. The solution must be sufficiently stable to give the product a reasonable shelf life; in the commercial world this would be at least two to five years. Cold stability must be displayed over the wide range of temperatures encountered by products being moved in commerce without the need for special handling such as heated transport or storage facilities. Furthermore, the active ingredient itself must display chemical stability over this same period of time. The Propoxur insecticide of the present application, for instance, is subject to hydrolysis in water, particularly if the system is slightly alkaline. In addition, the viscosity of the final formulation must be sufficiently fluid to allow ready application and be sprayable, particularly from finger pump sprayers. Such sprayable formulations should not form a stable foam on being sprayed. Finally, the formulation should have a reasonable concentration of active ingredient so as to maintain an acceptable ratio of packaging cost to amount of active ingredient and so as not to require that an inordinate amount of formulation be applied to obtain effective insect control.
A water based formulation utilizing approximately 0.5 wt. % of Chlorpyrifos (Dursban or Phosphorothioic acid O,O-diethyl O-(3,5,6-dichloro-2-pyridinyl)ester) as the active ingredient has been introduced to the market in a pressurized spray can. This material is an emulsion, a disperson of a dissolved pesticide in a petroleum solvent, being dispersed in water with the aid of an emulsifier. It is not a true solution and must be shaken to be reconstituted. It must also be protected against freezing temperatures.
The propoxur active ingredient of the present application has been disclosed in U.S. Pat. No. 4,285,968 in a water based formulation but the concentration of active ingredient was kept below 0.2 wt. %, because of solubility considerations, as the practical upper limit.